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November 2015

Angling for an Answer

PNNL researchers find fast, accurate method to compare climate effects


A team led by PNNL has introduced a new method of comparing climate-changing factors in climate models by directly comparing their climate responses.
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Results: There are many factors that can change the climate, like human-caused emissions, naturally-occurring gases, and even heat radiated from the Sun. Though it is well known that each contributing factor has a different effect on the climate, the challenge lies in finding out which effect is caused by which factor. Now, scientists at Pacific Northwest National Laboratory, Caltech and Lancaster University have established a technique using climate models to compare the factors to the effects they have on climate change by peering into climate models from a different angle.

"It's been known for a while that different sources, like carbon dioxide or methane, have different effects on our climate," said Dr. Ben Kravitz, climate scientist at PNNL, explaining the concept of radiative forcing. "Our new method turns the problem around. Instead of looking at the differences in the climate effects of two sources that add the same total energy to the climate system, we constrained the model so those sources had the same climate effects. Then, we figured out how much of each agent we needed to see the same climate effects." 

Why It Matters: Passing laws to regulate carbon dioxide emissions, methane emissions, or industrial particles could have an important effect on climate change. These different sources of emissions can have different effects, even if contributing the same amount of total energy on the climate. This new modeling technique allows scientists to view and compare the effects like never before. 

Methods: The research team extended the method to broader applications in understanding how the climate system works, and how it responds to changes in energy. The team increased one forcing agent (see sidebar) in a climate model, for example carbon dioxide, and decreased another, say methane, so that global mean temperature didn't change. The new method provides excellent comparisons of the forcing agents for a wide range of changes. Moreover, similar answers were found in different climate models, suggesting that this is a very simple way of ascertaining some of the mechanisms that can explain climate system response to climate change.

What's Next? Scientists tested this method for only three sources of change, but there are a whole host of things that can affect the climate. Each of those changes is represented differently in different models. Expanding this study to a larger range of sources, and getting more models involved will go a long way toward providing information on how the climate system works and how to better understand climate change.

Acknowledgments

Support: Aspects of this research were supported by the NASA High-End Computing Program through the NASA Center for Climate Simulation at Goddard Space Flight Center. Additional support provided by the Engineering and Physical Sciences Research Council.

Research Team: Ben Kravitz and Philip J. Rasch, PNNL; Douglas G. MacMartin, California Institute of Technology and Cornell University; and Andrew J. Jarvis, Lancaster University, UK.

Research Area: Climate & Earth Systems Science 

Reference: Kravitz B, DG MacMartin, PJ Rasch, and AJ Jarvis. 2015. "A New Method of Comparing Forcing Agents in Climate Models." Journal of Climate 28: 8203–8218. DOI: 10.1175/JCLI-D-14-00663.1.

November 2, 2015


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What is climate forcing?

Climate forcing consists of factors, naturally occurring and human-made, that contribute to a change in the Earth's energy balance affecting the climate. Natural factors come from sunlight, clouds, volcanoes and sea spray. Human-induced factors include increased greenhouse gases via burning fossil fuels, or changing land surfaces through deforestation or urbanization. In this research, they studied three common climate forcers: methane gas, the sun's rays, and car emissions. Ultimately, an increase in external climate forcing upsets Earth's natural energy balance.

In One Sentence: A team led by Pacific Northwest National Laboratory has introduced a new method of comparing climate-changing factors in climate models by directly comparing their climate responses.

In 100 characters: New technique compare factors that affect climate change by peering into climate models from a different angle

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